To improve flame retardancy of a thermoplastic resin composition is a major target to the research and development of the resin for a long time. It has been known the best method of using a halogen compound to prepare a flame retardant thermoplastic resin composition. U.S. Pat. Nos. 4,983,658 and 4,883,835 disclose thermoplastic resin compositions using a halogen compound as a flame retardant. The thermoplastic resin composition using a halogen compound shows good flame retardancy regardless of the base resin. However, the disadvantages could be observed that the halogen-containing compound results in the corrosion of the mold itself by the hydrogen halide gases released during the molding process and is fatally harmful due to the toxic gases liberated in case of fire. Therefore, halogen-free flame retardants have become a major concern in this field.
The representative halogen-free flame retardant is a phosphorous flame retardant nowadays. The phosphorous compound is superior to the halogen compound in corrosion of apparatus and toxic gas liberation. However, the phosphorous compound cannot provide better flame retardancy than the halogen compound, and, if more amount of the phosphorous compound is used to improve flame retardancy, the heat resistance is deteriorated. Furthermore, base resins are limited when the phosphorous compound is used as a flame retardant.
Another method to improve flame retardancy of a thermoplastic resin composition is add a material with good char formability to the base resin with poor char formability to form char film during combustion. The char film blocks transporting of oxygen, heat, and other fuel gases which could accelerate combustion of the resin.
As a phenol resin has a good char formability, it has been targeted to conduct a research of the flame retardant thermoplastic resin composition. However, the phenol resin has disadvantages that the intensity of the char film is not so strong, the phenol resin has a poor compatibility with other resin due to polarity of the resin, and a color change problem occurs because of weak weatherability.
Accordingly, the present inventors have developed a flame retardant thermoplastic resin composition that employs a phenol resin derivative which overcome the shortcomings above of the phenol resin. In the flame retardant thermoplastic resin composition according to the present invention, the phenol resin derivative solves the color change problem due to use of phenol resin and improves compatibility with other polymer resins. The phenol resin derivative provides the flame retardant thermoplastic resin composition with good char formability.